1. Field of the Invention
The present invention relates generally to methods for modulating cell adhesion, and more particularly to cyclic peptides comprising a classical cadherin cell adhesion recognition sequence, and to the use of such cyclic peptides for cancer therapy.
2. Description of the Related Art
Cancer is a significant health problem throughout the world. Although advances have been made in detection and therapy of cancer, no universally successful method for prevention or treatment is currently available. Cancer therapy currently relies on a combination of early diagnosis and aggressive treatment, which may include radiotherapy, chemotherapy or hormone therapy. However, the toxicity of such treatments limits the use of presently available anticancer agents. The high mortality rate for many cancers indicates that improvements are needed in cancer prevention and treatment.
Cell adhesion is a complex process that is important for tumor growth. Cell adhesion is mediated by specific cell surface adhesion molecules (CAMs). There are many different families of CAMs, including the immunoglobulin, integrin, selectin and cadherin superfamilies, and each cell type expresses a unique combination of these molecules. Cadherins are a rapidly expanding family of calcium-dependent CAMs (Munro et al., In: Cell Adhesion and Invasion in Cancer Metastasis, P. Brodt, ed., pp. 17-34, R G Landes Co.(Austin Tex., 1996). The classical cadherins (abbreviated CADs) are integral membrane glycoproteins that generally promote cell adhesion through homophilic interactions (a CAD on the surface of one cell binds to an identical CAD on the surface of another cell), although CADs also appear to be capable of forming heterotypic complexes with one another under certain circumstances and with lower affinity. Cadherins have been shown to regulate epithelial, endothelial, neural and cancer cell adhesion, with different CADs expressed on different cell types. N (neural)xe2x80x94cadherin is predominantly expressed by neural cells, endothelial cells and a variety of cancer cell types. E (epithelial)xe2x80x94cadherin is predominantly expressed by epithelial cells. Other CADs are P (placental)xe2x80x94cadherin, which is found in human skin and R (retinal)xe2x80x94cadherin. A detailed discussion of the classical cadherins is provided in Munro S B et al., 1996, In: Cell Adhesion and Invasion in Cancer Metastasis, P. Brodt, ed., pp.17-34 (R G Landes Company, Austin Tex.).
The structures of the CADs are generally similar. As illustrated in FIG. 1, CADs are composed of five extracellular domains (EC1-EC5), a single hydrophobic domain (TM) that transverses the plasma membrane (PM), and two cytoplasmic domains (CP1 and CP2). The calcium binding motifs DXNDN (SEQ ID NO:8), DXD and LDRE (SEQ ID NO:9) are interspersed throughout the extracellular domains. The first extracellular domain (EC 1) contains the classical cadherin cell adhesion recognition (CAR) sequence, HAV (His-Ala-Val), along with flanking sequences on either side of the CAR sequence that may play a role in conferring specificity. Synthetic peptides containing the CAR sequence and antibodies directed against the CAR sequence have been shown to inhibit CAD-dependent processes (Munro et al., supra; Blaschuk et al., J. Mol. Biol. 211:679-82, 1990; Blaschuk et al., Develop. Biol. 139:227-29, 1990; Alexander et al., J. Cell. Physiol. 156:610-18, 1993). The three-dimensional solution and crystal structures of the EC1 domain have been determined (Overduin et al., Science 267:386-389, 1995; Shapiro et al., Nature 374:327-337, 1995).
Interactions between cell adhesion molecules, such as classical cadherins, are responsible for binding of tumor cells to one another, as well as for angiogenesis (i.e., the growth of blood vessels from pre-existing blood vessels). Cancer tumors are solid masses of cells, growing out of control, which require nourishment via blood vessels, and the formation of new capillaries is a prerequisite for tumor growth and the emergence of metastases. Inhibition of undesirable cell adhesion mediated by classical cadherins has the potential to provide new therapeutic approaches for cancer therapy. However, to date, no such therapies are available.
Accordingly, there is a need in the art for improved cancer therapeutic agents that inhibit tumor growth by either modulating adhesion of cancer cells, or modulating the adhesion between the endothelial cells of both newly formed and pre-existing tumor blood vessels. The present invention fulfills this need and further provides other related advantages.
The present invention provides cyclic peptides and methods for modulating cadherin-mediated cell adhesion. Within one aspect, the present invention provides modulating agents that inhibit cadherin-mediated cell adhesion. Such agents comprise the sequence His-Ala-Val within a cyclic peptide ring. Within one embodiment a modulating agent comprises a cyclic peptide having the formula: 
wherein X1, and X2 are optional, and if present, are independently selected from the group consisting of amino acid residues and combinations thereof in which the residues are linked by peptide bonds, and wherein X1 and X2 independently range in size from 0 to 10 residues, such that the sum of residues contained within X1 and X2 ranges from 1 to 12; wherein Y1 and Y2 are independently selected from the group consisting of amino acid residues, and wherein a covalent bond is formed between residues Y1 and Y2; and wherein Z1 and Z2 are optional, and if present, are independently selected from the group consisting of amino acid residues and combinations thereof in which the residues are linked by peptide bonds. Such cyclic peptides may comprise modifications such as an N-acetyl or N-alkoxybenzyl group and/or a C-terminal amide or ester group. Cyclic peptides may be cyclized via, for example, a disulfide bond; an amide bond between terminal functional groups, between residue side-chains or between one terminal functional group and one residue side chain; a thioether bond or xcex41xcex41-ditryptophan, or a derivative thereof.
Certain modulating agents comprise a cyclic peptide having the formula: 
wherein Y is optional and, if present is selected from the group consisting of amino acid residues and combinations thereof in which the residues are linked by peptide bonds, and wherein Y ranges in size from 0 to 10 residues; and wherein X and Z are independently selected from the group consisting of amino acid residues, wherein a disulfide bond is formed between residues X and Z; and wherein X comprises an N-acetyl group.
Within specific embodiments, modulating agents as described above may be linked to a targeting agent and/or a drug. In addition, or alternatively, a modulating agent may further comprise one or more of: (a) a cell adhesion recognition sequence that is bound by an adhesion molecule other than a cadherin, wherein the cell adhesion recognition sequence is separated from any HAV sequence(s) by a linker; and/or (b) an antibody or antigen-binding fragment thereof that specifically binds to a cell adhesion recognition sequence bound by an adhesion molecule other than a cadherin.
The present invention further provides pharmaceutical compositions comprising a cell adhesion modulating agent as described above, in combination with a pharmaceutically acceptable carrier. Such compositions may further comprise a drug. Alternatively, or in addition, such compositions may comprise: (a) a peptide comprising a cell adhesion recognition sequence that is bound by an adhesion molecule other than a cadherin; and/or (b) an antibody or antigen-binding fragment thereof that specifically binds to a cell adhesion recognition sequence bound by an adhesion molecule other than a cadherin.
Within further aspects, methods for treating cancer and/or inhibiting metastasis of tumor cells in a mammal are provided, comprising administering to a mammal afflicted with cancer a cell adhesion modulating agent as described above.
Within related aspects, methods are provided for decreasing the size of a tumor in a mammal, comprising administering to a mammal having a tumor a cell adhesion modulating agent as described above.
These and other aspects of the invention will become evident upon reference to the following detailed description and attached drawings. All references disclosed herein are hereby incorporated by reference in their entirety as if each were individually noted for incorporation.